This invention is directed to a hydraulic control steering system and more particularly to a hydraulic control steering system for a rear caster wheel.
Work machines sometimes include one or more caster wheels which are carried by a machine frame and are free to rotate about a generally vertical axis 360°. As an example, self-propelled Windrowers are typically driven through a dual-path hydrostatic system. Speed changes are made by adjusting the speed of both drive (front) wheels simultaneously. Direction changes are made by adjusting the relative speed of the drive wheels. The rear wheels are castered to allow the machine to pivot during direction changes.
When direction changes are made, hydraulic pressure builds in one drive wheel circuit to increase speed and is reduced in the other drive wheel to lower the speed. The pressure difference continues until the inertia of the machine and the turn resistance of the casters are overcome. When turn resistance is high enough to create a delay in reaction to the steering wheel input, control of the machine can be difficult.
Due to the machine's inherent instability, the steering system is not ideal for high speed transport. Better machine control is needed at higher speeds without sacrificing the spin steer agility of the system at lower speeds. Also, improved machine handling is needed when towing an attachment. Thus, a control system is desired that addresses these deficiencies.
An objective of the present invention is to provide a control system that provides proportional steering control to rear caster wheels while also allowing for the wheels to rotate freely upon command.
Another objective of the present invention is to provide a control system that provides better machine control when towing an attachment.
A still further objective of the present invention is to provide better machine control and higher transport speed when driving on a road.
These and other objectives will be apparent to those skilled in the art based upon the following written description, drawings and claims.